1. Field of the Invention
The present invention relates to a semiconductor device and a fabrication method for the same.
2. Description of the Related Art
In recent years, along with miniaturization of LSIs, copper wires having low resistance (specific resistance is approximately 35% that of aluminum) and high electromigration tolerance are used as interconnect material for semiconductor devices since the sub-quarter micron age. Particularly, use of copper wires for the top layer interconnects required to carry a large current are very effective and are used for all multi-layered interconnects. However, copper is easily oxidized, and oxidation occurs not only in a hot atmosphere without a controlled oxygen concentration but also in atmospheric air. Once copper begins to oxidize, the oxidation continues deep into the copper without stopping at the surface, thereby corroding the entire copper interconnect. Therefore, in the case of bonding electrodes formed of copper wires, not only do the electrode surfaces become oxidized and lose adhesiveness with bonding wires, but corrosion of the oxidized electrodes due to interior oxidation progresses, and corrosion due to oxidation extends to the overall bonding wires and the copper wires.
As a result, when using copper as the interconnect material, technology for forming bonding electrodes using a material, instead of copper, that is resistant to oxidation is generally employed. FIG. 7 shows a conventional semiconductor device having bonding electrodes on top of copper wires. The bonding electrodes are made of a material resistant to oxidation (see Japanese Patent Application Laid-open No. 2003-31575 (p. 7, FIG. 7B), for example). The semiconductor device of FIG. 7 is formed through the processes described below. First, an interconnect pattern groove is formed in an insulating film 31 such as a silicon oxide film formed on a semiconductor substrate, a barrier metal 32 and a copper film 33 are deposited in the groove, and are then planarized using chemical mechanical polishing (CMP) so that only the copper film 33 remains in the groove. A diffusion preventive film 34 and an insulating film 35 such as a silicon oxide film are then deposited on the planarized area, forming an intermediate insulating film. An opening is formed in the diffusion preventive film 34 and the insulating film 35 or the intermediate insulating film so as to expose a part of the copper film 33.
Next, a barrier metal 36, which prevents a reaction from occurring between copper and aluminum, an aluminum film 37, and a barrier metal 38, which reduces reflectivity of the aluminum film 37 surface and allows lithography of an interconnect pattern, are successively deposited on the exposed part of the copper film and then removed through etching, except for a region in which a bonding electrode is supposed to be formed. Last, an insulating film 39 is deposited across the entirety and the insulating film 39 and the barrier metal 38 are selectively etched so as to expose the aluminum film 37, thereby forming a bonding opening 40 on top of the aluminum film 37. This completes the bonding electrode.
However, with the above invention, when the aluminum film is formed in the groove formed by etching the intermediate insulating film, there is a problem of poor coverage may occur ability since the groove is concave.
In order to improve this process, a semiconductor device has been manufactured in which a bonding electrode is formed by embedding a copper film in a groove formed in the intermediate insulating film layer to form a via, planarizing the top of the intermediate insulating film, depositing an aluminum film, and then etching.
However, with the two above-given processes of forming an aluminum film or a bonding electrode on such copper wires, cost has increased due to the fact that after the copper wires are formed, several additional processes such as forming an insulating film, a lithography process, and an etching process are necessary. Thus, the number of processes, until the bonding electrode is completed is increased.